The role of the gills in seawater adaptation inAnguilla dieffenbachii

Summary The mean serum sodium, chloride and potassium concentrations and serum osmotic pressure of freshwaterA. dieffenbachii are 140.4 mmol 1^–1,114.0 mmol 1^–1, 6.66 mmol 1^–1 and 307.7 mOsmol respectively. Gill tissue from freshwater specimens has a water content of 4234 mg g dry wt^–1 (80.9% wet wt), a chloride space of 1852 mg water g dry wt^–1 (35.2% wet wt) and an intracellular volume of 2449 mg water g dry wt (46.0% wet wt). Estimates of the intracellular sodium and potassium concentrations for the gill tissue of freshwater eels gave values of 28.9 mmol kg intracellular water^–1 and 126.5 mmol kg intracellular water^–1 respectively. On transfer of the fish to sea water serum concentrations of sodium and chloride and serum osmotic pressure show rapid initial increases followed by a more gradual decline eventually stabilising at new levels some 100 hours after transfer (Fig. 1). The serum sodium, chloride and potassium concentrations and serum osmotic pressure of seawater-adaptedA. dieffenbaehii are 162.8 mmol 1^–1, 151.0 mmol 1^–1, 6.70 mmol 1^–1 and 376.9 mOsmol respectively.On transfer to sea water the water content and chloride space of the gill tissue is reduced and the intracellular volume is initially decreased but is rapidly restored to its original value (Fig. 2, 3). At the same time intracellular sodium and potassium concentrations are increased but the latter is fairly rapidly restored to pre-transfer levels (Fig. 4).The changes in intracellular potassium concentration can be explained largely by the changes in intracellular volume but intracellular sodium concentrations remain high on transfer because of the increased serum sodium concentration. The initial increases in serum concentrations on transfer to sea water are caused partly by the removal of water and partly by the addition of sodium and chloride ions to the internal body fluids.     

Sea ice seasonality during the Holocene, Adélie Land, East Antarctica

Thin sections of laminated cores from different Antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale. Here we present the relative abundances of four diatom species and species groups (Fragilariopsis curta group as a proxy for yearly sea ice cover, F. kerguelensis as a proxy for summer sea-surface temperature, Chaetoceros Hyalochaete resting spores as a proxy for spring sea ice melting and the Thalassiosira antarctica group as a proxy for autumn sea ice formation) in core MD03-2601 retrieved off Adélie Land on the Antarctic continental shelf. These abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years. Both the marine records and the simulated climate demonstrated a cooler Early Holocene (9000–7700 years BP), a warmer Mid-Holocene (7700–4000 years BP) and a colder Late Holocene (4000–1000 years BP). Yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the Mid-Holocene Hypsithermal than during the Late Holocene Neoglacial. However, diatom census counts and model output indicate that sea ice spring melting happened earlier in the season, as expected, but that autumn sea ice formation also occurred earlier in the season during the Hypsithermal than during the colder Neoglacial, thereby following seasonal changes in local insolation.     

Seaweed succession on artificial reefs on different bottom substrata

Artificial rest reefs were set on sandy and rocky bottoms at 5–10 m depth along the coast of southern Japan. Mature thalli ofSargassum, Gelidium and other seaweds were transported from other coastal areas, packed in mesh bags and attached to the reefs to start the beds. After one year, the seaweed flora on the reef on a sandy bottom consisted of more than 20 species, includingSargassum spp. andGelidium amansii, which are important animal food species. Coralline algae were the dominants on the rocky bottom reefs. The lower biomass on reefs on the rocky bottom was due to grazing by urchins. The same number of species was present in the first and second years on reefs on sandy bottoms, but there were moreSargassum thalli the second year.Maximum algal biomass of the artificial reef in May of the second year was 9998 g wet wt m^–2 in sandy areas, 441 g wet wt m^–2 in boulder areas and 228 g wet wt m^–2 in rocky areas. Reefs on rocky bottoms continued to be covered by coralline algae and several species ofCodium andDictyota.     

Summer biomass of a population of Iridaea cordata (Gigartinaceae,Rhodophyta) from Antarctica

Results of a seasonal study on biomass in an infralittoral population of Iridaea cordata from Terra Nova Bay (Ross Sea, Antarctica) are reported. Thalli were collected during the IX Italian Antarctic Expedition (austral summer 1993–94). The population studied is that living at depths of 4 to 6 m, where the highest density of plants occurred. The highest value of biomass (wet weight 3440 g m^–2) was found at the beginning of summer. In that period 72.5% of biomass was from 128 specimens belonging to weight classes 8 (>16 to 32 g) to 10 (>64 g), corresponding to 13.4% of the population in numbers. Small (<1 g) and medium (1 to 8 g) specimens provided the remaining biomass of 5% and 22.5%, respectively. During the month of January, the number of heavy specimens decreased. At the end of that month biomass reached a minimum of 2225 g m^–2. In February the biomass increased to 3169 g m ^–2, 72% of which was from 120 specimens belonging to weight classes 7 (>8 to 16 g) to 9 (>32 to 64 g), which numerically represented 18.5% of the population. Data showed that biomass depended mainly on the presence of large heavy specimens, even though they were always few in number. Moreover, the occurrence of such large thalli at the beginning of summer suggests that Iridaea cordata continues to grow during the long antarctic winter.     

Does uptake of Alexandrium fundyense cysts contribute to the levels of PSP toxin found in the sea scallop, Placopecten magellanicus?

Atlantic sea scallops, Placopecten magellanicus, in most areas of the Bay of Fundy, New Brunswick, Canada, have year-round concentrations of paralytic shellfish posioning (PSP) toxins greater than the regulatory concentration of 80 μg STX eq. 100 g⁻¹ wet weight. Scallops (mean shell height of 10.7 cm, age 3–5 years) were collected by SCUBA and individually tagged near Parker Island, Bay of Fundy. Half were hung 2 m below the low tide water level and the remainder were placed on the bottom (11 m depth at low tide) under the scallops held at 2 m. Scallop, water and sediment samples were collected monthly for determination of concentrations of PSP toxins and Alexandrium fundyense.In October, 1993, mean concentrations of PSP toxins in digestive gland, and mantle were 3205 and 1018 μg STX eq. 100 g⁻¹ wet weight, respectively. Eight months later (June 1994), PSP concentrations in digestive glands from the surface and bottom had declined to 504 and 682 μg STX eq. 100 g⁻¹ wet weight, respectively, whereas those in the mantle had declined to 802 and 681 μg STX eq. 100 g⁻¹ wet weight. During July 1994, A. fundyense concentrations observed at Parker Island and offshore were 320 cells l⁻¹ and 14,200 cells l⁻¹, respectively. Subsequently, toxin concentrations in surface and bottom scallop digestive glands increased to 12,720 and 11,408 μg STX eq. 100 g⁻¹ wet weight, whereas concentrations in mantles increased to 2126 and 1748 μg STX eq. 100 g⁻¹ wet weight, respectively. Concentrations of PSP toxins in these tissues in October 1994 were similar to those measured in October 1993. Concentrations of PSP toxin were less than the regulatory concentration in the gonads and non-detectable in adductor muscles of all scallops sampled.There were no statistically significant differences in profiles for uptake and depuration of PSP toxins in scallops held at the surface compared to those from bottom, suggesting that A. fundyense cysts at the concentrations found in the sediment (45 cysts cm⁻³) did not contribute significantly to the year-round presence of PSP toxins within scallop tissues. The year-round occurrence of PSP toxin is probably due to accumulation during summer blooms followed by a very slow rate of depuration.     

Canopy characteristics of the brown alga Sargassum muticum (Fucales,Phaeophyta) in Lake Grevelingen,southwest Netherlands

The present distribution of the invasive brown alga Sargassum muticum in the southwest Netherlands is updated. Populations of the alga were found to remain at their 1985 level in Lake Grevelingen, with a small eastward expansion into the Eastern Scheldt estuary. A new population for the brackish, non-tidal Lake Veere is reported. Within Lake Grevelingen S. muticum forms a persistent, extensive canopy of 100% cover (4,442.5 ± 525.6 g fresh wt m^–2, 640.3 ± 75.8 g dry wt m^–2) that has a marked effect upon the penetration of photosynthetically active radiation (PAR) (reduced by 97% at 0.1 m). Surface sea water temperatures can be elevated by 2.7 °C above water not associated with a Sargassum canopy; furthermore, the dense canopy shades and hence reduces water temperatures below 0.1 m depth. Productivity studies indicate that assimilation occurs in the upper levels of the canopy (57.09 µg C mg dry wt^–1 m^–2 at a mean PAR rate of 106.7 J cm^–2 h^–1). Self-shading and a resultant decrease in the rate of assimilation was evident below the canopy.     

Morphological characterization of the alimentary tract of Antarctic fishes and its relation to feeding habits

Summary Morphological and morphometric characteristics of the alimentary tract in 22 species of carnivorous antarctic fishes were studied. It is shown that all of these species have similar, well-developed Y-shaped stomachs with generally thick (0.5–1.0 mm) walls. The relative stomach lengths are also similar, ranging from 9.8 to 22.2% of body length. Relative intestine lengths, a characteristic frequently used as an indicator of the kind of food eaten by a species, are also remarkably similar among most species (31 to 67%). Notothenia gibberifrons, a conspicuous benthos feeder, has a significantly longer intestine (91%), probably as an adaptation to the quantity of undigestible material (mud) incorporated with its faunal prey. These values fit within or below the limits (60–150$) of relative intestine length described in the literature for carnivorous fishes. The number of pyloric caecae is in general relatively low and fairly constant in each species. It is concluded that the morphological features studied could represent similar adaptations of these antarctic fishes to a similar carnivorous diet.     

Annual net primary production calculated from eastern Canadian Irish moss fishery data

Western Prince Edward Island Irish moss (Chondrus crispus) has been intensively dragraked since 1966. As well, most unattached fronds removed by wave surge, ice, etc. are brought to shore by waves and currents, where they are harvested eagerly. Accurate annual fishing yields were recorded between 1966 and 1981 inclusive. Given that herbivore densities are reduced, likely due to the intensive raking, and that mean annual bycatch (non-Irish moss seaweeds) (23.4 %) and commercial bed sizes (873 ha) were known, the fishing yields thus were considered a unique database from which to calculate net primary production (NPP). Factors used to convert from wet to dry wt (DW), and from dry wt to carbon were 0.22 an 0.31, respectively. Calculated mean annual NPP values were as follows: 2.101 ± 0.654 t (DW) ha^–1 y^–1; 210.1 g DW m^–2 yr^–1 and 63.0 g C m^–2 yr^–1. These values are much lower than those calculated for northwest Atlantic kelp and rockweed but similar to that determined for northeast Atlantic Gracilaria verrucosa. The interannual variability pattern for NPP was similar for both the wild Irish moss harvest and that of experimental Chondrus crispus outplants placed in one of the 14 commercial beds.     

Ecogenetic studies on the function of pseudocholinesterase in serum of Antarctic species (Lobodon carcinophagus,Leptonychotes weddelli,Arctocephalus tropicalis and Aptenodytes fosteri)

Summary Pseudocholinesterase activity (EC 3.1.1.8, PCHE) is present in serum of antarctic species Lobodon carcinophagus, Leptonychotes weddelli, Arctocephalus tropicalis and Aptenodytes fosteri. Compared to humans, enzyme activities were low in these species, activities were more comparable to those of the other carnivora. Dibucaine hydrochloride in concentrations of 0.01 mmol/l inhibited PCHE activity to 100% whereas sodiumfluoride inhibited PCHE in only one crabeater seal by 9%. Under standard conditions fluoride (0.05 mmol/l) activated the enzyme of all investigated species by 27.2% (range: 2.7–82.4%). Average activation was 13% in male seals and 58% in female seals (t=4.06, P=0.02). It is suggested that activation of pseudocholinesterase by fluoride is necessary for antarctic species to warrant neurochemical function controlled by acetylcholinesterase (EC 3.1.1.7).     

Growth rates and agar properties of three gracilarioids in suspended open-water cultivation in St. Helena Bay, South Africa

Relative growth rates (RGRs), yields and agar characteristics of threegracilarioid isolates (Gracilariopsis sp. from St. Helena Bay, and Gracilaria gracilis isolates from Langebaan Lagoon and Saldanha Bay) weremeasured to assess the suitability of a site in St. Helena Bay for suspendedcultivation. The gracilarioids were grown on polypropylene ropes and`netlon' lines, and the RGRs were 4.0–11.0% d<sup>-1</sup> and 5.0–7.0%d<sup>-1</sup>, respectively. The RGR of the Langebaan isolate of G. gracilis grown on ropes was significantly higher than the RGR of otherisolates. The mean net yield for the Langebaan isolate grown on `netlon'lines was 2.6 ± 0.9 kg wet wt m^-2 30 day^-1. Thecultured gracilarioids were extracted for native and alkali treated agars. Themean native agar yield over the entire period was 39.0% dry wt. Alkalipretreatment reduced the yield by 55%, but significantly increased gelstrength. High gel strengths (>750 g cm^-2) were measured inagars from Gracilariopsis sp. and Saldanha Gracilaria gracilis inmid-summer and winter. The dynamic gelling and melting temperatures ofnative and alkali treated agars varied among the gracilarioids. The meangelling and melting temperatures of agars were about 39.0 ^°C and86.0 ^°C, respectively. The 3,6-AG content ranged from 29% to38% for native agars and 34–45% for alkali treated agars. While theseresults indicate that this site is suitable for gracilarioid cultivation, occasionallow-oxygen events in St. Helena Bay lead to production of hydrogensulphide in the sea water (`black tides'). Such events killed most inshorebiota (including seaweeds) in 1994 and 1998. This frequency (on average1–2 per decade) and duration (maximum 2 weeks) would have to beconsidered in planning commercial seaweed farming in St. Helena Bay.     

Population dynamics of Potamothrix alatus paravanicus Poddubnaya & Pataridze (Tubificidae) in different areas of Lake Sevan

Potamothrix alatus paravanicus Poddubnaya & Pataridze (Tubificidae) is the most abundant species of benthic invertebrate in Lake Sevan and the only species in the deep profundal. Differences in annual temperature, length of the stratification period (low oxygen content) and bottom sediment characteristics influence the population of P. a. paravanicus in different depth zones of Lake Sevan. From shallow to deep water a regular increase of the following indices was observed in 1984–1987: annual biomass from 1.2–2.0 to 8.2–17.0 g m^–2 wet weight; mean individual wet weight of clitellate specimens from 2.0–3.8 to 8.3–16.6 mg; total life span from one and a half to more than 20 years; the length of breeding season from 2–3 to 12 months.An important ecological distinction between P. a. paravanicus and allied Potamothrix hammoniensis (Michaelsen) is the much lower fecundity of the former species.     

A study of polynucleotide phosphorylase production by <Emphasis Type="Italic">Escherichia coli</Emphasis> in a hollow fibre reactor

A 30-l hollow fibre reactor with continuous fermentation for cell recycling of Escherichia coli AS 1.183 was used to remove the inhibitory effects on cell growth and extend the fast growth phase to increase the yield of polynucleotide phosphorylase (PNPase) in E. coli cells. When the dilution rate was 1.5 h⁻¹, the cell concentration of E. coli reached 235 g/l (wet wt, 70% moisture content), with PNPase activity above 90 u/g (wet wt). With the dilution rate is 1.0 h⁻¹, the fermentor volumetric productivity of PNPase in a hollow fiber reactor can reach 974 (u/h * l) compared to 20 (u/h * l) in a conventional batch culture.     

Effect of habitat structure on the feeding efficiency of young stages of razor fish (Pelecus cultratus (L.)): an experimental approach

The effects of a submerged macrophyte (Potamogeton pectinatus), turbidity (produced by 50 mg l^–1 kaolin), and their combination on the feeding rate of young razor fish (Pelecus cultratus (L.)) were studied in the laboratory. Young razor fish showed preference for Copepoda in most of the simulated habitats. Razor fish fed more efficiently in the absence of any environmental structure, but the more structured habitats, 3 g wet wt l^–1 of simulated submerged macrophyte and turbidity combined with vegetation, had a negative impact on food consumption rates.     

Seasonal dynamics of rotifer and crustacean zooplankton populations in a eutrophic,monomictic lake with a note on rotifer sampling techniques

The abundances, biomass, and seasonal succession of rotifer and crustacean zooplankton were examined in a man-made, eutrophic lake, Lake Oglethorpe, over a 13 month period. There was an inverse correlation between the abundance of rotifers and crustaceans. Rotifers were most abundant and dominated (>69%) the rotifer-crustacean biomass during summer months (June–September) while crustacean zooplankton dominated during the remainder of the year (>89%). Peak biomasses of crustaceans were observed in the fall (151 µg dry wt l^–1 in October) and spring (89.66 µg dry wt l^–1 in May). Mean annual biomass levels were 46.99 µg dry wt l^–1 for crustaceans and 19.26 µg dry wt l^–1 for rotifers. Trichocerca rousseleti, Polyarthra sp., Keratella cochlearis and Kellicottia bostoniensis were the most abundant rotifers in the lake. Diaptomus siciloides and Daphnia parvula were the most abundant crustaceans. Lake Oglethorpe is distinct in having an unusually high abundance of rotifers (range 217–7980 l^–1). These high densities can be attributed not only to the eutrophic conditions of the lake but also to the detailed sampling methods employed in this study.The research was supported by National Science Foundation grants DEB 7725354 and DEB 8005582 to Dr. K. G. Porter. It is lake Oglethorpe Limnological Association Contribution No. 25 and Contribution No. 371 of the Harbor Branch Foundation, Inc.     

Variation in the carbon content of two Asplanchna species

The rotifers of the genus Asplanchna were sampled four times during the summer from eight lakes of different types. The mean individual carbon content in the population varied between 0.15–0.66 µg C ind.^-1 (n = 21) for A. priodonta and 1.0–1.6 µg C ind.^-1 (n = 3) for A. herricki. The carbon content and the size of A. priodonta varied considerably between the populations of both different lakes and dates.The carbon level of both Asplanchna species (sample mean 0.2–1% of wet weight) was considerably lower than is generally found for rotifers. Much of the variation of carbon level could be explained by an inverse relationship with wet weight. The high variation in the carbon content of individuals suggests that Asplanch population may adapt their mean body size to fit prevailing environmental conditions.     

Ecdysteroids in nemerteans: Presence and physiological role

Ecdysteroids were detected in the phylum Nemertea and their physiological role was studied. Radioimmunoassay (RIA) measurements showed ecdysteroid concentrations ranging from 1–47 pg/mg wet weight in several nemertean species from the orders Palaeonemertea, Heteronemertea, and Hoplonemertea. High-performance liquid chromatographic (HPLC) analysis of Paranemertes peregrina displayed peaks of RIA activity with retention times similar to those of authentic ecdysone and 20-hydroxyecdysone standards. Fluctuating ecdysteroid titers were observed in the various life stages of Carcinonemertes errans with the highest concentrations (47 pg/mg wet weight) found in gravid females. RIA of HPLC fractions of Carcinonemertes errans eggs indicated the presence of ecdysteroids (105 pg/mg wet weight). Alterations in the growth of juvenile, male, or female C. errans were not observed when the worms were exposed to 10^–7. 10^–6, or 10^–5 M 20-hydroxyecdysone. However, the eggs of C. errans appeared to be stimulated by 20-hydroxyecdysone. Shorter hatching times were observed in the egg strings exposed to hormone (10^–7 to 10^–5 M) compared to sea water and cholesterol (10^–11 and 10^–9 M) controls. Possible physiological roles and the evolutionary significance of ecdysteroids in nemerteans are discussed.     

Trophic significance of herbivorous macroinvertebrates on the central Great Barrier Reef

The common herbivorous macroinvertebrates on reef flats of the central Great Barrier Reef (GBR) were, in order of abundance: gastropod molluscs (Turbo and Trochus spp.); pagurid crabs; and the starfish, Linckia laevigata. The density of macroinvertebrates on Davies Reef was lowest in the thick-turf habitats at the windward reef-crest (0.6–0.9 m^–2) compared with 3.1 to 5.2 m^–2 elsewhere on the reef flat. Invertebrate grazer densities were similar on mid-shelf reef flats (mean: 2.3–3.6 m^–2) and significantly lower on outer-shelf reefs (0.3–1.0 m^–2). The ingestion rate of Turbo chrysostomus, the most abundant macroinvertebrate species, was derived from (a) faecal production and food absorption efficiency, (b) comparison of algal biomass on grazed and ungrazed natural substrata and (c) gut-filling rate and feeding periodicity in field populations. The ingestion rate of Trochus pyramis, the most common trochid and an abundant component of the macroinvertebrate fauna, was also estimated using (a). This gastropod fed continuously, whereas T. chrysostomus showed a distinct nocturnal feeding periodicity. T. chrysostomus and T. pyramis ingested daily means of 35 and 54 mgC animal^-1, respectively. Total gastropod grazing rates (mgC m^–2d^-1 in the field ranged from 11 in a thick-turf, reef-crest habitat to 144 on the open-grazed main flat. Grazing by gastropods accounted for between 0.3 and 8% of the net production of benthic algal food resources, depending on location on the reef flat. Across the whole reef flat the mean (areally-weighted) gastropod grazing rate was 6% of net production. A comparison of the relative roles of different types of grazers led to the conclusion that fishes are likely to have the greatest overall trophic impact on reefs of the central GBR. Even where macroinvertebrates are most abundant on reef flats, the yield from benthic algal communities to macroinvertebrates is estimated to be only one third of that due to fishes.Contribution no. 471 from the Australian Institute of Marine Science     

Carotenoid discrimination by the avian embryo: a lesson from wild birds

The concentrations (μg/g wet yolk) of total carotenoids in eggs of the common moorhen (Gallinula chloropus), American coot (Fulica americana) and lesser black-backed gull (Larus fuscus), collected in the wild, were 47.5, 131.0 and 71.6, respectively. In contrast to data for eggs of the domestic chicken, β-carotene was a significant component in the yolks of these three wild species, forming 25–29% by wt. of the total carotenoids present. The concentration of total carotenoids in the livers of the newly-hatched chicks was 5–10 times higher than in the other tissues and β-carotene was again a major component, forming 37–58% of the hepatic carotenoids. In the newly-hatched gull, the proportions of both lutein and zeaxanthin were very low in the liver but high in the heart and muscle when compared with the yolk. By contrast canthaxanthin, echinenone and β-carotene were very minor constituents of heart and muscle when compared with their proportions in the yolk of the gull. The proportions of lutein and zeaxanthin in the liver of the newly-hatched coot and moorhen were also far lower than in the yolk whereas the liver was relatively enriched with β-cryptoxanthin, β-carotene and (in the moorhen) echinenone. The results indicate that avian embryos discriminate between different carotenoids during their distribution from the yolk to the various tissues.     

Influence of environmental factors on the production of Potamothrix alatus paravanicus Poddubnaya & Pataridze (Tubificidae) in different areas of Lake Sevan

A modification of the Hynes' method was used to estimate production of Potamothrix alatus paravanicus Poddubnaya & Pataridze (Tubificidae), the dominant species of benthic invertebrate in Lake Sevan. Maximum production (5–24 g m^t\-2 wet weight) occurred in the sublittoral, while maximum biomass was found (8–17 g m^–2 wet weight) in the profundal. The turnover ratio of the average cohort varied between 2.4 and 5.0. The annual turnover ratio (P/B) decreased from 2.1–3.1 in the littoral to 0.1–0.4 in the profundal zone.A logarithmic correlation was found between P/B and temperature and oxygen regime, and depth and average size of clitellate specimens.     

Increased taxane accumulation in callus cultures of Taxus cuspidata and Taxus × media by some elicitors and precursors

In Taxus cuspidata callus, vanadyl sulfate (10 mg l^–1) induced a high (146 g g^–1 dry wt) production of 10-deacetylbaccatin III in comparison to 7 g g^–1 dry wt of the control. The content of paclitaxel in this species increased from 16 g g^–1 to 74 g g^–1 dry wt when 20 mg phenylalanine l^–1 was used. In T. media, p-aminobenzoic acid induced the highest content of 10-deacetylbaccatin III (481 g g^–1 dry wt) versus 181 g g^–1 in the control. Paclitaxel increased from 89 to 139 g g^–1 dry wt after adding chitosan (20 mg l^–1) to the cultures.